Method and apparatus for manufacturing monocrystalline articles

ABSTRACT

A method comprising pouring of molten metal into a mould, cooling of its base and subsequent cooling of the mould from the bottom up for crystallization of the melt. This method is carried out in an apparatus comprising a mould having a main cavity &#39;&#39;&#39;&#39;A&#39;&#39;&#39;&#39; following the shape of an article, and an auxiliary cavity &#39;&#39;&#39;&#39;B&#39;&#39;&#39;&#39; made in the form of a downwardly diverging truncated cone which has a horizontally extending wedge-shaped projection disposed at the lower base of the cone. The mould base is cooled by gradually moving a chill from the underside towards the mould. In so doing a sole natural nucleus of the article crystal is formed at the point of the wedge-shaped projection, which rapidly propagates over the perimeter of the base thereby preventing the formation of parasitic crystals.

Petrov et States Patent 1451 Dec. 31, 1974 Primary Examiner-Andrew R.Juhasz Assistant ExaminerJohn E. Roethel Attorney, Agent, orFirml-lolman & Stern [76] Inventors: Dmitry Andreevich Petrov, ulitsaChkalova, 21, kv. 80; Alexei Tikhonovich Tumanov, ulitsa B. [57]ABSTRACT s g k both of A method comprising pouring of molten metal intoa oscow mould, cooling of its base and subsequent cooling of [22] Filed:Feb. 13, 1973 the mould from the bottom up for crystallization of themelt. This method is carried out in an apparatus [21] Appl 332208comprising a mould having a main cavity A" following the shape of anarticle, and an auxiliary cavity B [52] US. Cl. 164/60, 164/361 made inh form f a downw rdly diverging truncated [51] Int. Cl B22d 25/06 onewhich has a horizontally extending wedge-shaped [58] Field of Search164/60, 122, 125, 126, projection disposed at the lower base of thecone. The 164/127, 361 mould base is cooled by gradually moving a chillfrom the underside towards the mould. In so doing a sole [56] ReferencesCited natural nucleus of the article crystal is formed at the UNITEDSTATES PATENTS point of the wedge-shaped projection, which rapidlypropagates over the perimeter of the base thereby pre- E2 g venting theformation of parasitic crystals. 315841676 6/1971 Busquet et al. 164/603,620,289 11/1971 Phipps 164/60 10 21 Draw Fgures PATENTED BEB3 1 I974SHEET 1 0F 5 PATENTEDBEE31 IBM 3'. 857, 43s

SHEET 2 OF 5 METHOD AND APPARATUS FOR MANUFACTURING MONOCRYSTALLINEARTICLES The invention relates to metallurgical production and moreparticularly to a method of manufacturing monocrystalline articles andcastings.

The invention may be used in manufacturing ingots and articles of metalsand alloys thereof with arbitrary or predetermined crystallographicorientation, such as blades for turbine engines, permanent magnets, etc.

Monocrystalline articles differ from conventional polycrystallinearticles primarily by the absence of boundaries between differently andarbitrarily oriented crystals, said boundaries often representing a weakzone during the operation of articles, especially at elevatedtemperatures. In addition, since crystals exhibit anisotropy, that is,their properties, especially magnetic and mechanical ones, depend uponcrystallographic orientation, optimum orientation of a crystal may beused when utilizing monocrystalline articles, said orientation impartingthe most improved characteristics to the article under operatingconditions. Studies show that the service life of monocrystalline bladesin a turbine engine is about four times longer at maximum operatingtemperature and about eight to ten times longer at moderate temperaturesas compared to that of polycrystalline blades, and the capacity ofmonocrystalline permanent magnets is about three to four times greaterthan that of the magnets having polycrystalline structure.

Known in the art is a method of manufacturing monocrystalline articlescomprising the pouring of molten metal into a mould, the base of themould being cooled, with subsequent crystallization proper by graduallycooling the mould from the bottom up after nucleation of many crystalsformed as a result of the coolmg.

In this prior art method a ceramic mould is used having a bottomcomprising a water-cooled metallic plate, the mould being attached tosaid plate by means of a flange and bolts.

Molten metal is poured into the mould. In so doing, a plurality ofsmall-size equiaxial crystals having an arbitrary crystallographicorientation are formed on the mould bottom as a result of abruptsupercooling of the melt, as it generally occurs during crystallizationof metal poured into a cold mould adjacent the walls and the bottomthereof.

The concurrent growth results in the survival of only the most rapidlygrowing crystals, which have the direction of growth parallel withrespect to the edge of a cubic crystal cell referred to as 001 incrystallography. These crystals are substantially parallel with eachother and grow normally to the surface of the water-cooled plate. Atsome distance from the plate the vertical cavity of the mould changesinto a horizontal cavity (construction), whereby the selection of thesecrystals which are adjacent to this transitory portion takes place.Columnar crystals are converted into plate crys tals. Then, by using thenext transistory horizontal cavity normal to the first one, one crystaladjacent to the transitory portion is withdrawn from this group of theplate crystals, and this crystal is introduced into the vertical cavityof a mould to form an article. Thus, a crystal seed having thecrystallographic direction 001 is actually selected, and an article,such as a blade for a turbine engine, is grown from this crystal seed.

This method exhibits a number of disadvantages, one of which consists inthat the articles can be produced only with one crystallographicorientation, namely 001. This excludes the possibility of obtainingarticles having other crystallographic orientations, such as 112, 111which could be better than those of the 001 orientation in regard to anumber of operational characteristics.

Furthermore, the entire system of transitory portions and cavitiesdisposed under the article-forming cavity is lost as waste material,that is its purpose consists solely in the selection of one crystal tobe introduced into the article-forming cavity of the mould. The samesystem of auxiliary cavities results in considerable distance betweenthe article and the chill thereby hampering intensive cooling of thearticle, whereby its mechanical properties are impaired.

It is an object of the invention to provide a method which ensures theproduction of monocrystalline articles by growing each time only onecrystal in a mould, the cavity of the mould following the article shapeand having no system of auxiliary transitory portions.

It is another object of the invention to provide an apparatus formanufacturing monocrystalline articles having any desiredcrystallographic orientation of the crystal.

The invention consists in the provision of a method and apparatus formanufacturing monocrystalline articles, wherein a mould adapted to bepoured with a melt of the article material and the conditions of coolingof this mould are such as to obtain an article grown directly from onecrystal nucleus formed on the mould bottom, with the crystallographicorientation of the crystal being predetermined in conformity with therequirements of the article.

The above object is accomplished by the method comprising pouring ofmolten metal into a mould having a flat horizontally extending base,said base being cooled from the bottom, with subsequent crystallizationproper by gradually cooling the mould from the bottom up afternucleation of a crystal formed as a result of cooling and itspropagation over the perimeter of the mould.

According to the invention a monocrystalline article is obtained in amould comprising two cavities: a top main cavity following the articleshape, and an auxiliary bottom cavity adjacent thereto and made in theform of a downwardly enlarging truncated cone, said cone having ahorizontally extending wedge-shaped projection at the lower-basethereof, a chill creating the conditions of the most abrupt supercoolingat the point of the projection so as to form a sole natural crystalnucleus and to ensure its rapid propagation over the perimeter of thebase.

Since the crystal is anisotropic, i.e., its properties in differentdirections depend upon the crystallographic orientation, then, in orderto obtain an article with absolutely definite and repeatedcharacteristics, it is necessary to manufacture it in a definitecrystallographic orientation. For this purpose, an artificial seed isintroduced into the place of formation of a natural seed.

The method according to the invention is carried out in an apparatuscomprising a mould adapted to be poured with a melt of the articlematerial, said mould having a flat horizontally extending base and achill arranged under the mould base in parallel therewith.

Artificial seeds may determine not only the axial orientation of anarticle but also orientation in the horizontal plane, which can affectthe characteristics of an article in its operation. I

According to the invention the mould comprises two cavities: a main topcavity following the article shape, and an auxiliary bottom cavityadjacent thereto and made in the form of a downwardly enlargingtruncated cone, said cone having a horizontally extending wedgeshapedprojection at the lower base thereof.

In order to achieve convenient accommodation of the article mould in aheated chamber and rational utilization of its volume, it isadvantageous that the auxiliary bottom cavities of at least two mouldsbe connected with the points of their wedge-shaped projections to form aconnection, with the point of this connection being located over thecentral part of the chill and representing the point of formation of asole natural nucleus of a crystal forming at least two articles eachhaving an identical crystallographic orientation.

The employment of the rods in the disclosed method is stipulated by thenecessity of cooling the article while operating, e.g., a turbine engineblade wherein the cooling is effected through the internal space of theblade formed by a special fire-proof rod placed into the model of anarticle. Then, the mold is made according to the model of the article.After manufacturing the mold, the model is removed by dissolution orsmelting, the rod remaining rigidly fixed in the mold by its one end.The other end of the rod being fitted is given certain freedom to ensureits movements under the effect of temperature.

Since the seed pocket is provided in the bottom of the mold and isprotruded downward, and a crystal seed is rabbled in said pocket, andfor giving birth to a crystal, the cooler should be brought into contactin its upper space with the bottom of the mold, said cooler is furnishedwith a seat to accommodate the seed pocket when the cooler is brought tothe bottom of the mold.

It is advantageous that a mould for a large-size article, which willoccupy the entire heated chamber, have two auxiliary cavities arrangedunder the main cavity, said cavities being connected at the point oftheir wedge-shaped projections, with the point of their connection beinglocated over the central part of the chill.

According to one embodiment of the invention an artificial nucleus isintroduced through a crystal seed at the point of formation of thenatural crystal nucleus, said artificial nucleus allowing for obtaininga crystal having a crystallographic orientation of the article axisdetermined by the artificial nucleus.

According to another embodiment of the invention a crystal seedcomprises a body of revolution cut from a crystal having a predeterminedcrystallographic orientation, the crystallographic plane of the crystalseed being set in parallel with the article axis by rotating said body.

Since the seed has a measurable length, it should be welded in its toppart to attain necessary contact with the smelt delivered into the moldand is preserved in a solid state in the lower part.

Still another embodiment of the invention consists in that at the pointof formation of the natural crystal nucleus the mould is provided with aseed pocket adapted to accommodate a crystal seed disposed normally tothe mould base.

According to a further embodiment of the invention a unit for coolingthe crystal seed is accommodated under the crystal seed in contacttherewith to control melting of the top of the crystal seed.

Another embodiment of the invention permits obtaining hollow articles byplacing a core into the mould, said core being removed upon completionof crystallization.

Where an artificial crystal nucleus is used, the apparatus according tothe invention comprises disposed at the central part of the chill arecess for a seed pocket with a crystal seed and for a unit for coolingthe crystal seed received in this recess during the upward movement ofthe chill.

The detailed description of the invention will now be made withreference to the accompanying drawings, in which:

FIG. I shows a diagrammatical generally longitudinal sectional view ofthe apparatus for manufacturing monocrystalline articles;

FIG. 2 is ditto, alternative embodiment;

FIG. 3 is a mould for manufacturing a monocrystalline ingot inlongitudinal section;

FIG. 4 is a diagram of a unit consisting of two moulds;

FIG. 5 is a diagram of a unit consisting of six moulds for manufacturingmonocrystalline blades for a turbine engine;

FIG. 6 is a diagrammatic view of a mould for manufacturing a large-sizearticle;

FIG. 7 is a plan view of an auxiliary cavity of a mould formanufacturing a monocrystalline ingot;

FIG. 8 is an auxiliary cavity of a mould for manufacturing amonocrystalline blade;

FIG. 9 is ditto, alternative embodiment;

FIG. It) is a turbine blade;

FIG. II is ditto, alternative embodiment;

FIG. 12 is a side view of the blade lock;

FIG. 13 is a side view of the blade airfoil;

FIG. M is a cylindrical monocrystalline ingot;

FIG. 15 shows cylindrical ingots made from one crystal nucleus in a unitconsisting of two moulds;

FIG. l6 shows cylindrical ingots made from one crystal nucleus in a unitconsisting of four moulds;

FIG. 17 shows two cylindrical monocrystalline ingots made from anartificial crystal nucleus introduced through a crystal seed;

FIG. 18 is ditto, with orientation in a stereographic triangle;

FIG. 19 shows orientation of ingots made in a unit consisting of twomoulds, in a stereographic triangle;

FIG. 20 shows orientation of ingots made in a unit consisting of fourmoulds in stereographic triangle; and

FIG. 21 shows two cylindrical monocrystalline ingots with crystal seedsmade in one unit therewith.

An apparatus for manufacturing monocrystalline articles comprises amould ll (FIG. I) enclosed by a graphite heating element 2 mounted onpower supply leads 3. The mould 1 comprises a main cavity A followingthe article shape, and an auxiliary cavity B adjacent thereto from thebottom. A chill 4 is arranged under the mould I. The mould I togetherwith the heating elements 2 and the chill 4 are placed in a vacuumchamber 5 having water-chilled walls. A vertical rod 6 adapted toreciprocate relative to the chamber 5 extends through the top cover ofthe chamber 5. The rod is provided with an internal passage for coolingwith water during the operation. A drive for the rod 6 comprises anelectric motor with a reduction gear (not shown). Mounted at the end ofthe rod 6 inside the chamber is a support member 7 adapted to fix themould 1 thereto. Extending through the bottom of the chamber 5 is avertical movable rod 8, the chill 4 being supported at the upper end ofthis rod inside the chamber 5. The rods 6 and 8 are coaxial. The chill 4comprises a flat horizontally extending plate cooled with water fedthrough a passage which is made in the rod 8 and communicates with apassage extending in the body of the plate of the chill 4. The rod 8 isalso driven by means of an electric motor and a reduction gear (notshown). The mould 1 is suspended to the support member 7 by means of anadapter 9 functioning as a grip for holding the mould 1. In order toobtain articles having a predetermined crystallographic orientation, acrystal seed is used. In this case the mould 1 (FIG. 2) for the articleis provided with a seed pocket 10 accommodating a crystal seed l1.

Mounted under the crystal seed 11 in the seed pocket 10 is a nut 12, aunit 13 for cooling the crystal seed 1 1 being fixed to said nut incontact with the lower end face of the crystal seed. The unit 13 forcooling the crystal seed 11 is adapted to remove heat from the crystalseed and to control melting of the top of the seed. In this case thechill 4 is provided at the central part thereof with a recess 14accommodating the seed pocket 10 with the crystal seed l1 and the unit13 for cooling the crystal seed 11. The depth of the recess 14 isdetermined by the size of the crystal seed 11 and of the unit 13 whichshould be completely received in the recess 14 so that the chill 4 cancontact the base of the mould 1 for conducting the crystallizationprocess.

The unit 13 for cooling the crystal seed 11 comprises a metalliccylinder, such as a copper cylinder, disposed in a sleeve 15 movablealong the generatric lines of the cylinder. Due to this embodiment thelengthof the unit 13 may be varied to adjust the distance between thebase of the mould l and the chill 4.

The mould 1 comprises two cavities: the main top 9 cavity A followingthe article shape, and the auxiliary bottom cavity B made in the form ofa downwardly diverging truncated cone, said cone having a horizontallyextending wedge-shaped projection at the lower base thereof. Thisprojection is formed by the method of inventment pattern during themanufacture of the mould 1. Accordingly, a fusible mass, such as amixture of paraffine and stearine, or urea is poured into a metallic diehaving a cavity following the shape and size of the article to beproduced. The resulting pattern is immersed into a dense binding mass,and then a layer of a finely divided granular material, such as electrocorundum is spread onto this mass through a sieve, after which drying iseffected. The immersion, spreading with granular material and dryingoperations are then repeated until eight to ten layers have beenapplied.

Then the pattern is melt out or dissolved, and the envelope is roasted.The resulting mould 1 should have a flat bottom of uniform thicknessover the entire surface area. This is required to ensure constant heatconductance of the bottom over the entire surface thereof.

The crystal seed 11 comprises a body of revolution, such as a cylinderor a cone cut from a single-crystal having a predeterminedcrystallographic orientation. Therefore, the crystallographicorientation of the crystal seed 11 is also predetermined. By rotatingthe crystal seed 1] about its axis the crystallographic plane thereofcan be set in parallel or at a predetermined angle with respect to thearticle plane.

The capacity of the chill 4 is selected depending upon the timenecessary to cool the base of the mould l and to supercool a melt of thematerial filling up the auxiliary cavity B thereof. If the chill 4 istoo powerful, it may not only result in cooling of the base of the mouldl, but also of the zones of the peripheral surface thereof adjacent tothe chill, which is not desirable. With low capacity of the chill 4 theprocess of supercooling of a melt of the material in the auxiliarycavity B of the mould l and the nucleation of a crystal will be toolong, which may disturb uniformity of the article singlecrystal as tocrystallographic orientation at the beginning of the growing thereof.

In order to obtain hollow articles, such as the blades for a turbineengine having a cavity for cooling, a core 16 is placed into the mouldl, the core following the shape of the internal cavity of the article.

The disclosed method enables also to manufacture hollow articles, e.g.,a turbine blade with air cooling, shown in FIG. 12 from the side of thelock and in FIG. 13 from the side of the upper bandage shelf.

The important feature of the method of manufacturing monocrystallinearticles consists in that a layer of melt poured into the mould I willbe the thinnest in the point of the wedge-shaped projection of theauxiliary cavity thereof. In addition, the heat conductance of the meltover the central part of the auxiliary cavity is substantially higherthan the heat conductance of the material of the mould 1 over the thinlayer of the melt at the point of the wedge-shaped projection.

Due to this fact, abrupt supercooling is carried out under the influenceof the chill 4 in the wedge-shaped projection, this supercoolinggradually diminishing along the perimeter of the base therebycontributing to the creation of a radial temperature gradient directedtowards the point thereof. All the above reasons contribute to thenucleation of a crystal at the point of the wedge-shaped projection ofthe mould l and to its rapid propagation over the perimeter of the base,whereby the nucleation of parasitic crystals in this zone is eliminated.

FIG. 21 shows two monocrystalline ingots (C) and (D) produced in oneunit with monocrystalline seeds (II). To manufacture such a unit, amodel is made up of two ingots with the models of seeds being connectedto them on a common base. The model assembled in such a manner is fed toproduce the mold.

The apparatus functions as follows.

The mould l accommodated in a vacuum chamber 5 is heated by means of theheating elements 2 at a tem perature above that corresponding to thebeginning of the melt crystallization.

Then a metal melted in a separate furnace is poured into the mould l.The temperature of the melt is checked by means of an immersionthermocouple immediately beforehand. The temperature of the melt at theinstant of its pouring into the mould 1 should be about l00- C higherthan the temperature corresponding to the beginning of crystallization,but somewhat lower than the temperature of the mould 1 so that after thepouring in the zone adjacent to the base the temperature should be about30- 40C lower than the temperature of the walls of the mould 1 at thesame altitude. When too overheated, the metal will require other coolingconditions, which may result in the for mation of parasitic crystalsadjacent the mould base.

During the heating of the mould I the chill 4 is spaced at such distancefrom the base thereof, that its cooling action upon the mould ispractically eliminated.

FIG. 6 shows a large-size article which, due to its large dimensions,can be manufactured only in the copy. In this case, two auxiliary spacesare arranged below the main space of the article, said two spaces beingconnected by the points of the wedge-shaped projections, and the placeof their connection being disposed above the central part of the cooler.FIG. 7 shows a plan view of the lower space of the article produced inthe mold whose drawing is given in FIG. 3. Symbol A denotes the upperbase of the article s space, and symbol B the lower base.

FIGS. 8 and 9 show a plan view of the lower space of the mold to producemonocrystalline blades depicted in FIGS. I and II respectively.

Upon pouring of metal into the mould I it is allowed to stay so during atime necessary for achieving the correspondence between the temperatureof the melt and the'mould 1.

By the end of the curing period the temperature of the melt immediatelyadjacent the base of the mould ll should about by 30- 40C higher thanthe temperature corresponding to the beginning of crystallization.

In order to effect the nucleation of a crystal the chill 4 mounted onthe movable rod 8 is fed towards the base of the mould I at a speedensuring its contact with the mould l at the instant, when thetemperature of the melt adjacent the base of the mould will become about30- 40C lower then the temperature corresponding to the beginning ofcrystallization. In this example the process continues for 10 12minutes.

At the instant of the contact between the chill 4 and the base of themould l the melt in the wedge-shaped projection of the auxiliary cavitythereof and slightly higher has been already solidified. Thus, duringthe period of gradual movement of the chill 4 towards the base of themould l a supercooling of the melt was created in the point of thewedge-shaped projection thereof and the formation of a sole crystalnucleus took place which subsequently propagated over the perimeter ofthe base of the mould ll.

Upon effecting the contact between the chill 4 and the mould l thelatter is disconnected from the support member 7, and the mould I on thechill 4 is gradually withdrawn by means of the rod 8 downwards from thezone of location of the heaters 2. The speed of movement of the chill 4with the mould ll supported thereon is determined by the article shape.

In order to avoid the formation of parasitic crystals on the articlesurface, the temperature of the walls of the mould I should bemaintained at a level higher than the temperature corresponding to thebeginning of solidification of the metal, which is achieved bymaintaining a temperature gradient in the metal, in this example ofabout l0/cm.

The crystal growth is controlled in such a manner that the melt-crystalinter-face that is the growth front be maintained at one and the samelevel relative to the heating element 2 of the mould I. This control iseffected by means of a thermocouple tracing the location of the growthfront, and the readings of the thermo couple must be constant until theend of the lowering of the mould 1 into the cold zone.

In this case, where hollow articles are to be produced, the core 16(FIGS. 12 and 13) placed into the mould I does not introduce any changesinto the formation and growth of the crystal nucleus. Thus, the crystalwhile propagating over the surface of the base of the mould 1, flowsround the core 16 from all sides. Upon the manufacturing of the articlethe core 16 is removed by the hydrodynamic or any other appropriatemethod.

If the crystal seed Ill is used for manufacturing an article, it isplaced into the seed pocket 10. The seed pocket 10 and the unit 13 forcooling the crystal seed 11 are being introduced into the recess 14 atthe central part of the chill 4 during the movement of the chill 4.Thus, the movable sleeve I5 moves upwards into alignment with the maincylinder of the unit 13 thereby reducing the length thereof. At theinstant of contact of the chill 4 with the base of the mould I the seedpocket 10 and the unit 13 are completely received in the seat 114 and donot interfere with this engagement.

Further process of the manufacturing of the article is performedsimilarly to the above-described embodiment.

In order to ensure more rational utilization of the volume of the vacuumchamber 5, at least two articles are generally made therein. In thiscase the auxiliary cavities of at least two moulds I are connected withthe points of their wedge-shaped projections to form a unit. The pointof connection is located over the central and the coldest part of thecooler 4. The moulds I are arranged symmetrically with respect to eachother. Four, six and more moulds may be connected in the similar manner.In this case the nucleation of a crystal takes place at the point ofconnection of the wedge-shaped projections, and the process continuessimilarly to the case, where a single article is produced.

Similar method may be used for manufacturing crystal seeds having apredetermined crystallographic orientation determined by an artificialcrystal nucleus (FIG. 21).

FIG. 15 shows cylindrical monocrystalline ingots obtained by the methodaccording to the invention in a unit consisting of two moulds.

FIGS. 19 and 20 illustrate the results of determination of thecrystallographic orientation of the ingots obtained in a unit consistingof two moulds I and in a unit consisting of four moulds 1 respectivelyby the Laue method. As it will be apparent from the both stereographictriangles, differences in orientation do not exceed two degrees in bothcases.

FIGS. 10 and Ill show turbine blades made by the method according to theinvention. FIG. 37 shows two cylindrical ingots C and D with a commonbase, said ingots having a crystallographic orientation predetermined bythe crystal seed I1.

FIG. 18 shows the result of determination of orientation of the bothingots as compared to the crystallographic orientation of the crystalseed II. The results are consistent within the range of two degrees.

Table I shows the results of determination of stressrupture resultsobtained during the tests of samples of a length of 38 mm and a diameterof 3 mm made of a highly refractory nickel-based alloy at 980C under aload of 21 kglmm Monocrystalline samples K, L. M, N and polycrystallinesamples 0, P, Q, R were tested after heat treatment, which consisted intheir exposure at 1220C for four hours, cooling in the air andsubseqauent ageing at 870C for 32 hours.

As it will be apparent from Table 1, the results of the tests of themonocrystalline samples K, L, M, N are considerably better than thoseobtained for the polycrystalline samples O, P, Q, R, both in regard totime to rupture, and elongation and reduction, which in the case ofmonocrystalline turbine blades corresponds to an increase in the servicelife of a turbine engine by 4 6 times.

What is claimed is:

l. A method of manufacturing monocrystalline articles comprising thesteps of pouring molten metal into a mould comprising a main top cavityfollowing the article shape and an auxiliary bottom cavity adjacentthereto and made in the form of a downwardly enlarging truncated cone,said cone having a horizontally extending wedge-shaped projection at thelower base thereof, which defines the base of said mould; cooling thebase of said mould by means for cooling thereof so as to create the mostabrupt supercooling of the melt at the point of said wedge-shapedprojection, to form at this point a sole natural crystal seed and toensure its rapid propagation over the entire perimeter of said base; andsubsequent gradual cooling of said mould from the bottom up to effectthe crystallization proper.

2. An apparatus for manufacturing monocrystalline articles comprising amould adapted to be poured with a molten article material; said mouldhaving a flat horizontally extending base; said mould having a maincavity following the article shape'and an auxiliary bottom cavityadjacent thereto and made in the form of a downwardly enlargingtruncated cone, said cone having a horizontally extending wedge-shapedprojection at the lower base thereof; a chill arranged under the base ofsaid mould in parallel therewith.

3. An apparatus according to claim 2, wherein the auxiliary cavities ofat least two moulds are connected at the points of their wedge-shapedprojections to form a unit, with the point of their connection beinglocated over the central part of the chill and representing the point offormation of a sole natural crystal nucleus forming at least twoarticles having an identical crystallographic orientation.

4. An apparatus according to claim 2, wherein the mould for a large-sizearticle has two auxiliary cavities disposed under the main cavity andconnected at the points of their wedge-shaped projections, the point oftheir connection being located over the central part of the chill.

5. An apparatus according to claim 2, wherein an artificial crystalnucleus is introduced at the point of formation of the natural crystalnucleus through a crystal seed, said artificial nucleus allowing forobtaining a crystal with the crystallographic orientation of the articleaxis predetermined by the artificial crystal nucleus.

6. An apparatus according to claim 5, wherein the crystal seed comprisesa body of revolution cut from a crystal having a predeterminedcrystallographic orientation, the crystallographic plane of the crystalseed being set in parallel with the article planeby rotating said body.

7. An apparatus according to claim 5, wherein a unit for cooling thecrystal seed is arranged under the crystal seed and in contacttherewith, said unit being adapted to control melting of the top of thecrystal seed.

8. An apparatus according to claim 5, wherein a mould is provided with aseed pocket disposed under the point of formation of the natural crystalnucleus and adapted to accommodate the crystal seed, said pocket beingarranged normally to the base of the mould.

9. An apparatus according to claim 2, wherein a core is placed into themould for obtaining a hollow article, said core being removed uponcompletion of crystallization.

10. An apparatus according to claim 8, wherein the chill is providedwith a recess at the central part thereof to accommodate the seed pocketwith the crystal seed and the unit for cooling the crystal seed.

1. A method of manufacturing monocrystalline articles comprising thesteps of pouring molten metal into a mould comprising a main top cavityfollowing the article shape and an auxiliary bottom cavity adjacentthereto and made in the form of a downwardly enlarging truncated cone,said cone having a horizontally extending wedge-shaped projection at thelower base thereof, which defines the base of said mould; cooling thebase of said mould by means for cooling thereof so as to create the mostabrupt supercooling of the melt at the point of said wedge-shapedprojection, to form at this point a sole natural crystal seed and toensure its rapid propagation over the entire perimeter of said base; andsubsequent gradual cooling of said mould from the bottom up to effectthe crystallization proper.
 2. An apparatus for manufacturingmonocrystalline articles comprising a mould adapted to be poured with amolten article material; said mould having a flat horizontally extendingbase; said mould having a main cavity following the article shape and anauxiliary bottom cavity adjacent thereto and made in the form of adownwardly enlarging truncated cone, said cone having a horizontallyextending wedge-shaped projection at the lower base thereof; a chillarranged under the base of said mould in parallel therewith.
 3. Anapparatus according to claim 2, wherein the auxiliary cavities of atleast two moulds are connected at the points of their wedge-shapedprojections to form a unit, with the point of their connection beinglocated over the central part of the chill and representing the point offormation of a sole natural crystal nucleus forming at least twoarticles having an identical crystallographic orientation.
 4. Anapparatus according to claim 2, wherein the mould for a large-sizearticle has two auxiliary cavities disposed under the main cavity andconnected at the points of their wedge-shaped projections, the point oftheir connection being located over the central part of the chill.
 5. Anapparatus according to claim 2, wherein an artificial crystal nucleus isintroduced at the point of formation of the natural crystal nucleusthrough a crystal seed, said artificial nucleus allowing for obtaining acrystal with the crystallographic orientation of the article axispredetermined by the artificial crystal nucleus.
 6. An apparatusaccording to claim 5, wherein the crystal seed comprises a body ofrevolution cut from a crystal having a predetermined crystallographicorientation, the crystallographic plane of the crystal seed being set inparallel with the article planeby rotating said body.
 7. An apparatusaccording to claim 5, wherein a unit for cooling the crystal seed isarranged under the crystal seed and in contact therewith, said unitbeing adapted to control melting of the top of the crystal seed.
 8. Anapparatus according to claim 5, wherein a mould is provided with a seedpocket disposed under the point of formation of the natural crystalnucleus and adapted to accommodate the crystal seed, said pocket beingarranged normally to the base of the mould.
 9. An apparatus according toclaim 2, wherein a core is placed into the mould for obtaining a hollowarticle, said core being removed upon completion of crystallization. 10.An apparatus according to claim 8, wherein the chill is provided with arecess at the central part thereof to accommodate the seed pocket withthe crystal seed and the unit for cooling the crystal seed.